The invention is generally related to methods for extracting an encapsulated device. More particularly, the invention is directed to methods for decapsulating semiconductor chips or dies.
Packaging, particularly plastic packaging, of various electronic devices including semiconductor chips or dies has been employed for some years. It is often desirous to decapsulate the device at least in part to allow for inspection, test, and repair of the device, as well as to provide xe2x80x9cbare diexe2x80x9d with which to build prototype systems.
Some current methods for recovering die from encapsulated packages involve the use of commercially-available decapsulators which generally employ heated, concentrated acids such as sulfuric and nitric acids or other solvents that dissolve encapsulant material surrounding the die. Problems with these decapsulators and methods include difficulty in achieving the desired amount of etching and difficulty preventing damage to the package including the die, bonding wires, and the metallization.
There are other disadvantages to current methods relating to the state of the die after the decapsulation process. Typically, wire bonds from the original package remain and must be removed, adding a critical step in the preparation of the die, increasing overall processing time and increasing the risk of failure of the process to yield usable die. Also, the top surface, or face, of the decapsulated die may be bare and/or uneven after conventional methods are performed, making proper subsequent handling more difficult and making subsequent processing steps such as lamination of the device more difficult or impossible. There is also the problem of vulnerability of the naked xe2x80x9cbare diexe2x80x9d whose face is substantially exposed after processing.
Conventional methods of die preparation include use of a lapping technique to grind packages to remove encapsulant. Generally, it is critical that the bottom surface of the die be free of irregularities so that the encapsulated die remains precisely parallel to the face of the lapping tool throughout grinding, otherwise the die may become damaged or destroyed. Current lapping techniques do not provide for adequate planarization of the base of the encapsulated die for many applications.
Accordingly, the invention provides improved methods of decapsulation.
It is an object of the invention to provide a convenient method of decapsulating a packaged die. In one embodiment, the method includes removing packaging material from a bottom section of a die-containing package to expose a die pan, removing the die pan, removing material between the die pan and the bottom surface of the die, using the bottom surface of the die to determine a grind plane substantially parallel to the top surface of the die, and removing packaging material from the top section of the die-containing package to form a top surface substantially planar to the grind plane, thereby enabling, for example, subsequent inspection, testing, and repair of the die, as well as enabling use of the xe2x80x9cbare diexe2x80x9d in prototyping applications. In other embodiments, the method of the invention provides for decapsulating a plurality of dies concurrently.
According to one embodiment of the invention in which a single packaged die is decapsulated, a first step grinds the packaging material at the bottom of a die-containing package until a die pan is exposed, using, for example, a conventional wafer grinding machine. Another step removes the die pan. A further step etches the packaging material and/or other material, such as the die attach, from about the bottom and sides of the packaged die, creating a channel in the packaging material around the perimeter of a newly-exposed base of the die. An additional step removes material from about the sides of the die by cutting along the channel around the perimeter of the die using, for example, a wafer dicing saw. According to one feature, the exposed base of the die, with die pan and die attach removed, provides a highly planar mounting surface, which the method employs to determine a grind plane passing through a top section of the die-containing package. In one embodiment, the grind plane passes through wire bonds attached to a top surface of the die. Another step employs a conventional lapping technique to grind the top portion of the packaged die down to a level substantially parallel to the grind plane. In one embodiment, the top portion of the packaged die is ground sufficiently to expose the wire bonds on the top surface of the die.
According to a further feature, the invention preserves a passivation layer of packaging material of appropriate thickness such that it does not interfere in the operation of the die, but provides for protection of the die throughout subsequent handling and use. According to another feature, a substantially planar passivation layer provides a good surface for facilitating lamination of the die. An advantage of the inventive process is that it obviates the requirement of acid contact on the top surface of the die, thus preventing harm to components of the die, such as the die metallization, resulting from conventional decapsulation methods.